The present invention relates to an electrical circuit for supplying voltage to an electrode for starting, maintaining and quenching an arc between the electrode and a conductive member.
A portable manganese determinator in which a hand held probe utilizes an arc generating electrode when positioned against a specimen material is disclosed in U.S. Pat. No. 3,791,743 issued Feb. 12, 1974 to Thomas E. Cody et al. In such a system, an electrical arc is generated between the electrode and a conductive sample against which the probe is positioned vaporizing enough of the specimen for subsequent analysis by a flame photometer. In this system, a DC voltage is applied to the electrode which is moved into engagement with the surface of the specimen to be analyzed and subsequently backed off to a gap of approximately 1.2 mm to start and maintain the arc. The electrical circuit used for supplying the electrode power according to the teachings of this patent employs a constant current source and a delay circuit for controlling the amplitude and duration, respectively, of current applied to the electrode for controlling the arc.
Although such a system provides adequate results, the electrode is actuated by a voltage of about 50 V DC at all times and can be a shock hazard, particularly when the instrument is employed out of doors and in rainy or wet weather which occasionally occurs. This voltage, while sufficiently high to be a shock hazard is not high enough to sustain a good quality arc against many steels including, for example, stainless steel, with a relatively low conductivity.